1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, a transflective type LCD device for selectively using a reflective mode and a transmitting mode, and a method for manufacturing the same.
2. Discussion of the Related Art
In general, LCD devices are classified into two types, a transmitting type LCD device and a reflective type LCD device. At this time, the transmitting type LCD device has a backlight as a light source, so that the transmitting type LCD device can produce a picture image in the dark. However, it has the problem of high power consumption. Meanwhile, the reflective type LCD device uses ambient light as a light source, so that it has lower power consumption. However, the reflective type LCD device has a limitation in that it cannot display a picture image in the dark. In order to solve these problems, a transflective type LCD device is disclosed. The transflective type LCD device can operate as a reflective type or a transmitting type as needed with the transflective LCD having both a reflective part and a transmitting part inside a unit pixel region. That is, the transflective type LCD device selectively uses ambient light or artificial light, whereby it is possible to operate the transflective type LCD device independent of the surrounding environment and to decrease power consumption.
Meanwhile, the LCD devices may have an additional storage capacitor for maintaining an electric charge across the pixel. A structure forming a capacitor between a preceding gate line and a pixel electrode is referred to as a storage-on-gate structure. The storage capacitor maintains a voltage across a liquid crystal during a turn-off mode of a corresponding thin film transistor. Accordingly, during the turn-off mode of the thin film transistor, it is possible to prevent a current from leaking, thereby preventing picture quality degredation due to flicker.
Hereinafter, a general transflective type LCD device will be described with reference to the accompanying drawings.
FIG. 1 is an exploded perspective view illustrating some parts of the general transflective type LCD device. As shown in FIG. 1, the general transflective type LCD device 11 includes an upper substrate 15, a lower substrate 21, and a liquid crystal 23 between the upper substrate 15 and the lower substrate 21. Herein, a color filter 17 having a black matrix 16 is formed on the upper substrate 15, and then a common electrode 13 is formed on the color filter. The lower substrate 21 includes a pixel region P, a pixel electrode 19 having a transmitting part A and a reflective part C in the pixel region P, a switching device T and array lines. The lower substrate 21 is referred to as a TFT array substrate, in which a plurality of gate lines 25 are formed substantially perpendicular to a plurality of data lines 27, thereby forming a plurality of thin film transistors T as the switching devices in a matrix. At this time, the pixel region P is defined by the crossing of the gate lines 25 and the data lines 27.
The operational characteristics of the aforementioned transflective type LCD device will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view illustrating a general transflective type LCD device. As shown in FIG. 2, the general transflective type LCD device 11 includes an upper substrate 15 having a common electrode 13, a lower substrate 21 having a pixel electrode 19 including a transmitting electrode 19a and a reflective electrode 19b having a transmitting hole A, a liquid crystal 23 charged between the upper substrate 15 and the lower substrate 21, and a backlight 41 below the lower substrate 21. When the transflective type LCD device 11 having the aforementioned structure is used in a reflective mode, the ambient light is used as a light source.
Hereinafter, the operation of the transmitting mode or reflective mode LCD device will be described with reference to the aforementioned structure.
In the reflective mode, the LCD device uses ambient light as the light source, in which the light B is incident on the upper substrate 15 of the LCD device, and then reflected by the reflective electrode 19b. Subsequently, the light passes through the liquid crystal 23 arranged by an electric field between the reflective electrode 19b and the common electrode 13, so that a picture image is displayed by controlling the transmittance of the light B passing through the liquid crystal 23 according to the arrangement of the liquid crystal 23. Meanwhile, in the transmitting mode, the backlight 41 is used as the light source for emitting the light F. The backlight 41 is formed below the lower substrate 21, of which the light F is emitted from the backlight 41, and incident on the liquid crystal 23 through the transparent electrode 19a. Thus, a picture image is displayed by controlling the transmittance of the light from the backlight 41 through the liquid crystal 23 as arranged by an electric field between the transparent electrode 19a and the common electrode 13 below the transmitting hole.
A related art transflective type LCD device and a method for manufacturing the same will be described with reference to the accompanying drawings. In general, an LCD device includes a lower substrate of a thin film transistor array substrate, an upper substrate of a color filter substrate, and a liquid crystal between the upper substrate and the lower substrate. At this time, the lower substrate of the thin film transistor array substrate will be described in more detail.
A transflective type LCD device and a method for manufacturing the same according to a first method of the related art will be described as follows. FIG. 3 and FIG. 4 are respectively a plan view and a cross-sectional view illustrating a transflective type LCD device according to the first method of the related art. FIG. 5A to FIG. 5C are sequential plan views illustrating an enlarged pixel of an array substrate in a method for manufacturing a transflective type LCD device according to the first method of the related art. FIG. 6A to FIG. 6C are cross-sectional views taken along lines I-I′, II-II′ and III-III′ of FIG. 5A to FIG. 5C for illustrating manufacturing process.
As shown in FIG. 3 and FIG. 4, the transflective type LCD device according to the first method of the related art includes a gate line 31, a gate electrode 31b, and a lower storage electrode 31c. The gate lines 31 are formed on a transparent substrate 30 at fixed intervals in one direction substantially parallel to one another, and each gate electrode 31b is projected from each of the gate lines 31 at one direction. Then, the lower storage electrode 31c is formed integral with the preceding gate line corresponding to a storage capacitor. After that, a gate insulating layer 32 is formed to electrically insulate the gate line 31, the gate electrode 31b, and the lower storage electrode 31c from an upper layer, and an active layer 33 is formed on the gate insulating layer 32 above the gate electrode 31b. In this state, the active layer 33 is formed of an amorphous silicon layer, and an ohmic contact layer 33a of doped amorphous silicon is formed on the active layer 33 except for a channel region.
Next, a data line 34 is formed to be substantially perpendicular to the gate line 31, thereby defining a pixel region. A source electrode 34b is projected from the data line 34 in a direction overlapping with one side of the active layer 33, and a drain electrode 34c is formed to be apart from the source electrode 34b overlapping with the other side of the active layer 33. Then, an upper storage electrode 34d is formed at the preceding gate line integral with the drain electrode 34c above the lower storage electrode 31c. 
Subsequently, a first passivation layer 35 is formed on an entire surface of the substrate 30 including the drain electrode 34c and the upper storage electrode 34d. At this time, the first passivation layer 35 has first, second, and third contact holes 36a, 36b, and 36c respectively formed above the upper storage electrode 34d, gate and source pads 31a and 34a, and a transmitting hole 36d in the pixel region. Then, a reflective electrode 37 is formed in the pixel region except on a lower surface of the transmitting hole. At this time, the reflective electrode 37 is partially overlapped with the data line 34 defining the pixel region. Also, a second passivation layer 38 is formed on the entire surface of the substrate 30 except the first, second and third contact holes 36a, 36b, and 36c and the lower surface of the transmitting hole 36d. Next, a gate pad terminal 39a and a source pad terminal 39b are formed above the first and third contact holes 36a and 36c and the adjoining second passivation layer 38, and a transmitting electrode 39c is formed in the pixel region having the transmitting hole 36d for being in contact with the upper storage electrode 34d through the second contact hole 36b. In the pixel region, the transmitting electrode 39c is in contact with the upper storage electrode 34d through the second contact hole 36b, and a pixel electrode is formed of the reflective electrode 37 and the transmitting electrode 39c. 
In the method for forming the transflective type LCD device according to the first method of the related art, referring to FIG. 5A and FIG. 6A, a conductive metal material such as aluminum Al, molybdenum Mo, tungsten W or conductive alloy is deposited on the transparent substrate 30, and then patterned to form the gate pad 31 a having a predetermined area at an end thereof, the gate line 31 extended from the gate pad 31 a in one direction, and the gate electrode 31b projected from the gate line 31 to have a predetermined area. When forming the gate line 31, the lower storage electrode 31c is formed in the storage capacitor region of the gate line. Next, an insulating material such as silicon dioxide SiO2 or silicon nitride SiNx is formed on the entire surface of the substrate 30. Also, the amorphous silicon layer having amorphous silicon a-Si and impurity is deposited to form the gate insulating layer 32 and a semiconductor layer (amorphous silicon and doped amorphous silicon). After that, the semiconductor layer is patterned to form the active layer 33 with an island-shape above the gate electrode 31b. 
Subsequently, a conductive metal material such as molybdenum Mo, tungsten W or chrome Cr is deposited on the entire surface of the substrate 31 having the active layer 33, and then a patterning process is performed thereon. According to the patterning process, the data line 34 is formed substantially perpendicular to the gate line to have the gate insulating layer 32 in between, the source pad 34a is formed at one end of the data line 34, and the source electrode 34b projected to the upper side of the gate electrode 31b is formed overlapping with one side of the active layer 33. When forming the data line 34, the drain electrode 34c apart from the source electrode 34b is formed overlapping with the other side of the active layer 33, and the upper storage electrode 34d is formed as integral with the drain electrode 34c above the lower storage electrode 31 of the preceding gate line. Also, the doped amorphous silicon of the channel region is etched by using the source electrode 34b and the drain electrode 34c as masks, whereby the ohmic contact layer 33a is formed on the active layer 33.
As shown in FIG. 5B and FIG. 6B, an organic insulating material such as benzocyclobuten BCB or photoacrylic resin is formed on the entire surface of the substrate including the upper storage electrode 34d, thereby forming the first passivation layer 35. After patterning the first passivation layer 35, the transmitting hole 36d is formed in the pixel region. Then, a reflective metal having low resistance and great reflectivity is deposited on the first passivation layer 35 including the transmitting hole 36d, and patterned to form the reflective electrode 37. Subsequently, a silicon nitride layer SiNx is deposited on the substrate 30 including the reflective electrode 37 to form the second passivation layer 38. By etching the second passivation layer 38, the reflective electrode 37, and the gate insulating layer 31c, the first, second, and third contact holes 36a, 36b and 36c are respectively formed above the upper storage electrode 34d, the gate pad 31a, and the source pad 34a. At this time, the portion of the substrate 30 corresponding to the transmitting hole 36d is exposed.
Referring to FIG. 5C and FIG. 6C, a transparent conductive metal such as Indium-Tin-Oxide ITO or Indium-Zinc-Oxide IZO is formed on the entire surface of the substrate 30 including the source electrode 34b and the drain electrode 34c, and then a patterning process is performed thereto. As a result, the transmitting electrode 39c is formed in the pixel region in direct contact with the upper storage electrode 34d at the preceding gate line. When forming the reflective electrode 37, the gate pad terminal 39a is formed on the contact hole of the gate pad 31a and the adjoining second passivation layer 38 in contact with the gate pad 31a, and the source pad terminal 39b is formed on the contact hole of the source pad 34a and the adjoining second passivation layer 38 in contact with the source pad 34a. At this time, the reflective electrode 37 is partially overlapped with the data line 34 defining the pixel region.
A transflective type LCD device according to a second method of the related art and a method for manufacturing the same will be described as follows. FIG. 7 and FIG. 8 are respectively a plan view and a cross-sectional view illustrating a transflective type LCD device according to the second method of the related art. FIG. 9A to FIG. 9C are sequential plan views illustrating an enlarged pixel of an array substrate in a method for manufacturing a transflective type LCD device according to the second method of the related art. FIG. 10A to FIG. 10C are cross-sectional views taken along lines IV-IV′, V-V′ and VI-VI′ of FIG. 9A to FIG. 9C for illustrating the manufacturing process.
Referring to FIG. 7 and FIG. 8, the transflective type LCD device according to the second method of the related art has the same structure as the transflective type LCD device according to the first method of the related art except that a second passivation layer 55b (circle portions in FIG. 7) having projections is formed on a first passivation layer 55a of a reflective part (pixel region except a transmitting hole 56d), and a reflective electrode 57 has an uneven surface on the second passivation layer 55b. In the method for forming the transflective type LCD device according to the second method of the related art, referring to FIG. 10B and FIG. 10C, the second passivation layer 55b is deposited on a first passivation layer 55a, and then an exposure and developing process is performed thereto to form projection patterns in the second passivation layer 55b corresponding to a reflective part.
However, the transflective type LCD devices according to the first and second methods of the related art have the following disadvantages. In the methods for forming the transflective type LCD device according to the first and second methods of the related art, it is necessary to form the contact hole in the upper storage electrode formed integral with the drain electrode for connecting the pixel region to the drain electrode, such that the aperture ratio is decreased in the reflective part forming the contact hole. Also, in the transflective type LCD device according to the second method of the related art, it is hard to form the projection patterns corresponding to the number of the contact hole regions in the upper storage electrode, whereby the aperture ratio of the reflective part becomes lower than that according to the first method of the related art.